In recent years, non-volatile memories that are data-rewritable semiconductor devices are widely used. Multi-level cell (MLC) memories have a plurality of memory cells, each being divided into a left half cell and a right half cell. Each of the left half cell and the right half cell may store multi-bit, for example but not limited, 2 bits. During writing data into MLC memories, second bit effect in one half cell may be serious if there is too much charge trapped in the other half cell. Further, in reading distribution, if one distribution is too wide, the related sensing window(s) may be negatively affected.